Automatic telephone exchange



E. H. CLARK ET AL AUTOMATIC TELEPHONE EXCHANGE June 24, 1930.

Filed Sept. 29, 1.928 11 Sheets-Sheet l olIllU Ls mm w A TTDH/VE) June 24, 1930. E. H. CLARK ET AL 1,767,960

' AUTOMATIC TELEPHONE EXCHANGE Filed Sept. 29, 1928 11 Sheets-Sheet 2 I a mi I L 00m h. 62A RA HREN W 0A RPEA/TE/i June 24, 1930, CLARK ET AL 1,767,960

AUTOMATIC TELEPHONE vEXCI'HNGE Filed Sept. 29 1928 11 Shets-Sheet 3 /Nl/EN 727/951 m aw am ATTORAf? June 24, 1930. H, CLARK ET AL. 1,767,960

AUTOMATIC TELEPHONE EXCHANGE Filed Sept. 29, 1928 11 Sheets-Sheet 4 EDGAR hfCLA/wr WVEVTUHS' MRHEN W CARPENTE BY (9%? J7);

June 24, 193g. E. H. CLARK AL 1,767,960

AUTOMATI C TELEPHONE EXCHANGE Filed Sept. 29, 1928 11 Sheets-Sheet 5 EDGARH BLAH/g WVENTUHS' MRRENWUAHPE/ ER "arrow/2 i June 24, 1930. R H, LA'RK'ET AL 1,767,960

AUTOMATIC TELEPHONE EXCHANGE Fi1ed Sept.29, 192a llishgets-sheet fDBA/i" H GLAR/r RHEA/ W CARPENTER June 24, 1930.

E. H. CLARK ET AL AUTOMATIC TELEPHbNE EXCHANGE Filed Sept. 29, 1928- llISheets-Sheet 7 fDGA/P H CLARK 5y RREN I44 UAR/ 5mm? @QMQQEQI wmawgmfi an June 24, 1930. CLARK ET AL 7, 1,767,960

AUTOMATIC TELEPHONE EXCHANGE 'Filed se t'. 29, 1929 11' Sheets-Sheet -8 EDGAR H 6 WVENTOHS' MRREN W CARPENTER June 24, 1930. E. H. CLARK ET AL I I AUTOMATIC TELEPHONE EXCHANGE 11 Sheets-Sheet 9 Filed Sept. 29, 1928 //V VENTUES. M

09m H CLARK REE/V W CARPENTER Arm/way June 24, 1930. CLARK ET AL. EflZQQ AUTOMATIC TELEPHONE EXCHANGE 1 Filed Sept. 29, 1928 ll Sheets-Sheet l0 June 24, 1930.

E. H. CLARK E AL 1,767,960

AUTOMATIC TELEPHONE EXCHANGE Filed Sept. 29, 1928 11 Sheets-Sheet ll I II IIII IIII III 5054/? h. CLARK WVENTORS' WARREN W CARPENTER ATTDRNY Patented June 24, 1 930 iterate Parana tries EDGAR H. CLARK, or ronns'r HILLS, Ann WARRE w. CARPENTER, or QUEENS VILLAGE, NEW Yoax, assrenoias '10 BELL TELEPHONE. LABORATORIES, moon- PORATED, or nnwronx, n. Y., A CORPORATION on NEW YORK Application filed September 29, 1928.

This invention relates to telephone ex change systems and particularly to those systems wherein mechanical switching apparatus is employed in the establishment of connections between subscribers lines terminating in manual offices of the exchange area and subscribers lines terminating in machine switching oflices of the same area.

The invention has for its object the simplification of apparatus necessary for the establishment of such connections and the increased economy in the first cost and maintenance thereof.

In exchange areas which are being changed through the installation of machine switching apparatus to operate on a full mechanical basis rather than on a strictly manual basis, it is desirable that provision be made for the extension ofcalls originated in a manual ofiice of the exchange to any of the outlying automatic offices through the control of the selector switches in the called automatic cities, by mechanism located at the calling manual oiiice. As the exchange area becomes more nearly full mechanical through the changing of a greater number of the manual otfices to automatic otfices, the need for such control equipment for the remaining manual-ofiices becomes more essential. By this plan the operator who first answers the call is enabled to establish the interofiice connection which leads to a distant automatic oiiice without assistance, the entire operation of the switches at the distant automatic oifice being governed by mechanism at the originating office controlled by the answering operator therein.

This has been accomplished satisfactorily in the past by circuits of the type shown, for example, in Patent 1,513,862, issued October 28, 1924 to L. M. Allen. The present invention was developed to attain the same results as have been heretofore attained in the employment of circuits of the type disclosed in this patent with simpler apparatus and with greater economy.

Serial no. 309,175.

In accordance with the present invention, one embodimnt of which has been disclosed herein, by way of example, each manual ofiice is provided with a plurality'of operators positions, each of which hasaccess to a plurality of groups of outgoing trunks, one group leading to each of the automatic otlices of the exchange area. Each position is further equipped'witha sender controlling key board, a set of office keys and office code register relays, and a set of relay registers and indicatin lamps for trunk identification purposes. In order that an idle sender common to all operators positions may be taken for use to extend a call and asso ciated with the key board and registers of the operators position concerned, each sender is provided with two step-by-step position finders individual theretowhich mutually hunt forand associate a calling operators position therewith. In order that the selected sender may become associated with an idle trunk to the desired automatic oi'iice, each sender is associated with a first'selector switch individual thereto which in turn has access either directly or through second solector switches to all of the trunks in the difi'erent groups extending to the several automatic ofiices.

In the operation of the system, the operator who answers an incoming call at the originating manual oflice first depresses an office key at her position corresponding to the office in which the desired line terminates and thereby causes the position finder switch associated with an idle sender to hunt for her position and to associate her position apparatus with such sender, and causes the registration of the ofiice code designation of the desired line on the oifice code register relays of her position.

' She may then depress keys in her keyboard to register on the numerical registers of the sender the numerical designation of the desired line. The tens designation of'the ofiice code is then transferred toa code register in the sender and, assuming that both first and second selectors are to be used, the first selector switch is set under sender control in accordance therewith, and thereupon hunts for an idle second selector to further extend the connection from the sender to the desired interofiice trunk group. Thereafter the units designation of the office code is transferred to the code register of the sender which is now instrumental in setting the second selector switch whereby a group of trunks to the desired office is selected. The second selector is operated further in hunting movements to find a sub-group of trunks to the desired oflice and an idle link in the selected sub-group. Such selective movements being registered in the sender, which in turn controls the setting of the trunk number indicating relays of the position apparatus to indicate to the operator the number of the selected outgoing trunk.

' If the trunk group to the desired office terminates in a terminal bank of the first selector, such first selector only is controlled by the sender to extend a connection from the sender to an idle trunk of such group of trunks.

The operator then plugs into the jack of the indicated trunk and her position apparatus is freed for another call. then proceeds to operate the selector switches in the selected automatic office in accordance with the numerical designation registered on the registers thereof in the well known manner.

Referring to the drawings, Figs. 1 to 10, inclusive, arranged in accordance with the diagram of Fig; 12, disclose so much of a telephone system embodying the'principles of this invention as is necessary to a comprehensive understanding thereof.

Fig. 1 shows one of a pluralityof answering operators positions of a manual office provided with cord circuits for extending subscribers lines over inter-office trunks outgoing to distant dial switching ofiices. One of these outgoing trunks terminating in a dial switching office is illustrated in this figure.

Fig. 2 shows a set of numerical keys, one

- ofiice key, a portion of the ofiice code registers, and control relays of the operators position shown in Fig. 1. V

Fig. 3 shows pair of position finder switches individual to the sender of Figs. 5, 6, 7 and 8 for associating the operators position equipment of Figs. 2 and 4: with such sender.

Fig. 4 shows a trunk number indicating equipment individual to the operators posi tion of Fig. 1 for indicating to the operator the number of the inter-ofiice trunk over which a connection to the-desired dial switch ing office is to beextended and also shows a group of transfer relays. 7

.Figs. 5, 6, 7 and 8, taken together show one The sender of a plurality of register senders available for the use of all operators positions of one manual office. Fig. 5 shows two steering switches of the sender. Fig. 6 shows control relays. Fig. 7 shows relay registers for registering the numerical digits of wanted line numbers and Fig. 8 shows control and counting relays for setting the switches of the dial switching office under the control of the registers of Fig. 7, counting relays for controlling the setting of the trunk number indicating equipment of Fig. 4:, and ofiice code register relays. r

Fig. 9 shows a first selector individual to the sender and Fig 10 shows one of a plurality of second selectors for connecting a selected sender with an idle trunk extending to a desired dial switching ofice.

Fig. 11 shows diagrammatically the arrangeinent'oi start circuits for a plurality of 7 pairs of position finders, such as the pair shown in Fig. 3.

12 is a diagram showing how the various figures should be arranged with relation to each other.

The selector switches 123 and 124. diagrammatically illustrated in Fig. 1 and located in the distant dial switching ofiice 122 are of the well-known power driven type, such as are shown in the patent to 'E. B. Craft and J. N. Reynolds No. 1,223,396, granted January 5, 1915. More particularly, they are of the specific type fully disclosed and described in the patent to F. A. Stearn and F. J. Scudder No. 1,395,977, granted November 1, 1921 The steering switches 509 and 550 of Fig. 5 are of the rotary single motion step-by-step type driven by stepping magnets from terminal to terminal and so arranged that the brushes are moved forward to the next set of terminals upon the deenergization of the corresponding stepping magnet.

The selector switches of Figs. 9 and 10 and the position finder switches of Fig. 3 are of the step-by-step type having both a vertical and a rotary motion. Each switch is pro-.

vided with a pair of brush sets and corresponding banks of terminals. More specifically, these switches are of the type disclosed in Patent No. 1,700,4l66, granted to V. JV. Carpenter Jan. 29, 1929.

The operators position equipment shown in Fig 2 comprises a set of ten non-locking digit keys 211 upon which the operator may write up the numerical digits of wanted line numbers, a plurality of cities keys only one of which 200 has been illustrated and two groups of ofiice code relays, only one relay of each group having been disclosed. As many oiiice keysare provided at each position as there are dial switching ofiices in the exchange area to which the manual oflice has access. Each such group of code register relays comprises eight relays, only the first of each group having been disclosed, the register relays of one group register the tens codeletter of an office designation, and the relays of the other group register the units code letter. By suitable interconnections with the office keys it is possible by the depression of a single key to register the first two letters of any office designation. For example, as will be hereinafter more fully described, the depression of key 200 registers the oliice code CA for the office CAnal on the tens register relay 202 and on the units register relay 201. g

It is believed that the invention will be best understood from a detailed explanation of the manner in which a connection may be established. To this end it will be assumed that the subscriber of line in the manual oflice wishes to converse with the subscriber of line 125 in a distant dial switching office 122. Upon removing his receiver from the switchhook, the calling subscriber completes a circuit for the energization of line relay 1041, which in turn causes the illumination of lamp 105. The operator upon observing the illumination of lamp answers by inserting the plug 102 of one of her cord circuits in the jack 101. The insertion of the plug in the jack completes a circuit from battery through.

the lamp 107, resistance 106, sleeves of plug 102 and jack 101, winding of relay 103 to ground. Relay 103 operates and severs the circuit of relay 10 1 which causes the line lamp 105 to become extinguished. The receiver being off the switchhook the insertion of the plug in the jack also completes a circuit from battery through the lower left winding of repeating coil 109, the winding of relay 110, rings of plug 102 and jack 101 over the loop of the line, returning over the tips of jack 101 and plug 102, upper left winding of repeating coil 109 to ground. Relay 110 operates in this circuit and closes a circuit from battery through its contact, resistance 108, resistance 106, thence over the path previously traced through the winding of relay 103 to ground. This latter circuit shunts the lamp 107 causing the same to remain extinguished. The operator neXt depresses the listening key 112 connecting her headset into conversational relation with the calling line and ascertains the wishes of the calling subscriber.

Upon learning that he wishes to talk With a subscriber at a distant office 122, the operator depresses the office key 200 of Fig. 2,

which key corresponds to such distant office. 1

For the purposes of this description it will be assumed that'the wanted line number is UAnal 3981 and that therefore upon the depression of key 200, the No. 2 units code register relay 201 is operated over a circuit extending from battery through the left winding of relay 201, the left contact of key 200 to ground at the right back contact of relay 203 and that the tens code register relay 202 is operated over a circuit from battery 203, the front contact of relay 204 to ground at the outer left contact of relay 201, but relay 203 does not operate in this locking circuit until the key 200 is released. Upon the release of key 200, relay 203 energizes opening at its back contacts the initial operating circuits'of relays 201 and 202 and of all other register relays of the position to prevent interference with a call should the operator depress another office key before a call has been completed and her position'equipment released. The code register relays prepare circuits for the transfer of the oiiice code number to the sender as will be hereinafter described. I

Association of an idle sender with the operators position Relay 201 upon energizing establishes a circuit for relay 206 extending from battery through the winding of relay 206, the outer rfght contact of relay 207 to ground at the outer left contact of relay 201, a circuit for relay 208 extending from battery through the winding thereof over the inner right contact of relay 207 to ground at the outer left contact of relay 201, and a circuit for lamp 209 extending from battery through said lamp, the back contact of relay 210, the left back contact of relay 207 to ground at the outer left contact of relay 201. Lamp 209 burns steadily at this time and relay 208 upon energizing connects the contacts of the keys of key set 211 over conductor 220 to battery through the right winding of relay 210. Should the operator prematurely depress a key of the key set, that is, while the lamp 209'is burning steadily denoting that a sender has not yet been associated with her posiwill flicker as a signal that the operator should release her position and start the call over. She may do this by depressing release key 222 thereby operating release relay 205 which, in turn, releases all operated relays of the position. Relay 208, upon operat- Fig.3

ing, also dissociates the key contacts of key set 211 from conductors 223 to 226, inclusive, extending to the position finders of Fig. 3.

Relay 206 upon operating, at its left contact prepares an operating circuit for the cut-off relay 207 extending to conductor 22? and at its right contact establishes an obvious circuit for the group relay 228. By referring to Fig. 11 it will be noted that provision is made for 100 operators positions, said positions being subdivided into ten groups of ten positions each. Each subgroup of ten positions has common thereto a group start relay 228. In Fig. 11 the individual start relays 206 and 206 and cut-off relays 207 and 207 of the first and tenth positions of the first subgroup and the individual start relays 206 and 206 and cut-oil relays 207 and 207 of the 91st "and 100th positions in the tenth sub-group of positions together with their corresponding group relays 228 and 228 lave been illustrated. lnasmuch as it is necesary extend ele en con trol conductors from the operators position equipment to a sender and as a line finder of of the type employed is provided with but six brushes, it is necessary to provide two line finders, arranged to operate in parallel, individual to each sender. A pair of such position finders individual to a sender such as shown in Figs. to 8, inclusive, is provided for normally serving each 'roup of ten positions, but the start circuits are so arranged, as shown in Fig. 11, that a pair of finders individual to any idle sender may be made available to serve any one of the 100 positions. Referring to Fig. 3 in which one pair of such finders is disclosed for normally serving the group of positions in which the position of Fig. 2 is located, one finder of the pair is disclosed above the dot and dash line having rotary magnet 300, vertical magnet 301, release magnet 302, off-normal contact 303, commutator brush 302 and brushes 305 and 310, inclusive, and the other of the pair is disclosed below the dot and dash line having rotary magnet 320, vertical magnet 321, release magnet 322, off-normal contacts 323 and 32 1 and brushes 325 to 330, inclusive. The relays shown in the dotted rectangle of are common to all pairs of position finders. 1 V

l/Vhen, therefore, the group relay 228 of the sub-group in which the position equipment of Fig. 2 is located operates, assuming that the pair of finders normally allotted for serving such sub-group is idle, a circuit is extended from battery through the winding of relay 311, the make-before-break contacts of relay 312, transfer key 3 14:," conductor 313, the left contacts of relay 228, conductor 314 to ground at the left back contact of relay 312. Relay 228 at its outer right contact also connects ground over a conductor, such as 315, to place a calling potential on the commutator of the upper position finder of each pair corresponding to the bank level thereof in which the sub-group of positions appearand at its inner right front contact connects ground to conductor 316 for operating the common relay 317. Belay 317 energizes, in turn, operating the common relay 318 in a circuit extending to ground at the back contacts of all relays similar to relay 312 of line finder pairs that are at the time idle.

Relay 318, upon operating, furnishes locking battery for the relay of each position inder pair corresponding to relay 312 for a purpose to be later explained. Relay 311, upon operating, establishes a circuit for relay 319 entending from battery through the right winding thereof, the back contacts of magnets 300 and 301, the front contactof relay 311 to ground at the outer right back contact of relay 331. Relay 319 operates in this circuitand looks from battery through its right windingand inner right contact, over the back contacts of magnets 320 and 321, the outer left alternate contact of relay 319 to ground at the outer right back contact of relay At its outer right contact relay 319 establishes a circuit for vertical magnet 301 of the upper finder extending from battery, winding of magnet 301, the right back contact of relay 332 to ground at the outer right contact of relay 319, and at its inner left contact establishes a circuit for magnet 321 extending from battery, through such magnet, the left back contact of relay 332 to ground at the inner left contact of relay 319. ltfagnets 301 and 321 both energize, magnet 301 opening the initial energizing circuit of relay 319 and magnet 321 opening the locking circuitthereof. WVhen therefore both vertical magnets are completely energized and the finder shafts have been advanced vertically one step, relay 319 releases, in turn opening the operating circuits of magnets-301 and 321.

it will be assumed that the calling opera tors position terminates in the first bank level of each of these finders and that therefore when the finders have been stepped to this level, ground potential placed upon commutator terminal 333 by the group relay 228 will be encountered by the commutator brush 304 and a circuit will be completed therefrom over conductor 335 through the right winding of relay 332 to battery through the right winding of relay 319 before the vertical magnet 301 releases. Relays 319 and 332 thereupon energize relay 319 locking itself operated over its right winding and inner right contact, the back contacts of magnets 320 and 321, the outer alternate left contact'of relay 319, the front contact of relay 311 to ground at the outer right back contact of relay 331, and relay 332 locking itself from battery, over its left winding and inner left contact to ground at the-outer right back contact of relay 331. With relays 319 and 332 both energized circuits are now established for the rotary magnets 300 and 321 extending from battery through the winding of magnet 30.0, the right front contact of relay 332 to ground at the outer right contact of relay 319, and from battery through the winding of magnet 320, the outer left front contact of relay 332 to ground at the inner left contact of relay 319. Magnets 300 and 320 both energize, advancing the brushes of both finders one step in a rotary direction. The energization of magnet 320 now opens the locking circuit of relay 319 and since its initial energizing circuit vas opened at the commutator brush 30 1, as soon as the upper finder rotated one step, relay 319 deenergizes opening the operating circuits of magnets 300 and 320. These magnets, in turn,

deenergize again closing an operating circuit for relay 319 extending from battery through its right Winding, the back contacts of magnets 300 and 301, the'front contact of relay 311 toground at the outer right back contact of relay 331. Relay 319 again energizes and looks as before and, establishes the operating circuits of magnets 300 and 320. In this manner magnets 300 and 320 and relay 319 reciprocally operate-t0 advance the brushes of the position finders in a rotary hunting move ment.

When the brushes have been so advanced to the terminals associated withthe calling operators equipment, a circuit becomes established from battery, winding of cut-ofi relay 207, the left contact of relay 206, conductor 227, test terminal 352, test brush 309, the winding of relay 3 10, the right normal contacts of relay 331 to ground, through the left windingof relay 319, thereby differentially releasing relay 319 and energizing relays 207 and 340. Relay 207, upon energizing, locks over its Winding and inner left front contact, the outer left back contact of relay 205 directly to conductor 227 independently of relay 206, opens at its right contacts the circuits of relays 206 and 208, thereby releasing said relays and at its outer left front contact establishes a circuit from ground through the slow interrupter 230 over the right back contact of relay 210 to battery through the lamp 209. Lamp 209 now flashes to indicate that the operators position has been attached to an'idle sender and that she proceed to operate the keys of keyboard 211 to set the numerical registers of such sender to record the numerical designation of the desired line. The release of relay 206 opens the circuit of group relay 228 which, in turn, releases, releasing relays 311, 317 and 318, the two latter relays releasing only in case there is no other call initiated at the, time.

Relay 340, upon operating, closes obvious circuits over its left contact for relays 331 and341 which upon operating extend control circuits from the operators position equipment over brushes 305 to 308, 310 and 325 to 330, inclusive. At its right back contact relay 331 opens the holding circuit of relay 332, the circuit previously traced through the right winding of relay 319 and at its right makebefore-break contacts substitutes direct ground in the circuitof relays 207 and 340 in place of ground through the left winding of relay 319. Relay 332 thereupon releases. At its intermediate right contact relay 331 also closes a circuit extending from ground over such contact, conductor 3 12, winding of relay 621, conductor 626 to battery. A circuit is also established in parallelwith relay 621 from ground on conductor 342, over conductor 718, the winding of relay 700, conductor 719 to battery on conductor 626. l

Relay 621 upon energizing prepares several circuits. At its intermediate'right contact it establishes a circuit for relay 805*extending from ground over conductor 502, brush 503 and the first position terminal of steering switch 550, conductor 501 to battery through the winding of relay'805. At its inner right contact relay 621 connects ground to conductor 509 for furnishing locking ground to relays of Figs. 5,6 and 8. At its inner left contact relay 621 connects ground over conductor 801, through the winding of relay 800,0onductor 902, off-normal terminals 901 of the first selector of Fig. 9 to battery through the left winding of relay 900. Relay 900 energizes in this circuit, but relay 800 does not. Relay 900, upon operating, closes a locking circuit for itself extending over its left winding and left contact to the front contact of relay 915, which latter relay energizes upon the energization of relay 700 over a circuit extending from battery through the winding of relay 915, conductor 702 to ground at the innermost lower front contact of relay 700. Relay 915 also at its backcontact opens one point in the operating circuit of the release magnet 917 of the first selector. Relay 805, upon energizing, in the circuit previously traced connects locking groundover its inner front contact to conductor 806 for furnishing locking ground for the counting relays and operating ground for the relays of group 825 of Fig. 8. At its outer right front contact relay 621 also closes a circuit for stepping magnet 5120f the steering switch 550 extending from battery through the winding of magnet 512 over conductor 513, the next to the outer front contact of relay 805, the back contact of counting relay'802, conductor 815, the outer front contact of relay 621, conductor 604 first position terminal and brush 51 1 of steering switch 550, conductor 515 to ground at the inner right back contact of relay 600, prepar atory to advancing the stering switch into position 2. At its outer left contact relay 621 also closes a locking circuit for itself extendin from battery on conductor 626,

lowermost front contact establishes a circuit extending from ground over conductor 7 22 to battery through the left winding of relay 312. Relay'312 thereupon ener 'izes, looking over its left winning and inner left front contact and off normal contact 324 to ground, removes ground at its left back contact from the start conductor. 314, removes ground at its right back contact from the common conductor 343 and at its inner right make-before-break contacts extends the starting conductor 313 to the start relay corresponding to relay 311 of the pair of position finders associated with the next idle sender.

It will be explained at this point how another call, initiated at a position of the same sub-group, is able to associate anothe idle sender with suclrposition. For this purposeit will be assumed that upon the de pression of an oliice key at such other posi tion,.for example, the tenth position of such sub-group, relay 206 disclosed in Fig. 11 becomes energized, in turn, operating the common group relay 228. It Will further .be assumed that the next idle sender is the sender normally assigned for serving positions 91 to 100, inclusive. Referring to Fig. 11' with relay 312 energized as justdescribed, a circuitis now established from ground at the lower back contact of relay 312 associated with the pair of position finders individual to such idle sender, over the com mon conductor 314 the lower front contact of group relay 228, conductor 31 3 transfer key 344, the front contact of relay 312, thence in a chain circuit t rough the front contacts of other relays similartorelay 312 associated with position finders of other busy senders, thence to transfer key 34 the normal contact of relay 312 to battery through the winding of start relay 311. Start relay 311 upon operating starts the pair of position finders associated with the idle sender in the manner previously described. So long as thereis an initiated call at any position and any group relay such as 228 is energized relay 317 remains energized, in turn, maintaining relay 318 operated until all senders have been taken for use, since relay 318 receives operating ground over common conductor 343 and a back contact of the relay 312 of the position finders associated witl each idle sender. lVith relay 318 energized,

even'though the sender which was taken for use by a previously initiated call in that sub-group should become idle. Since relay 312 cannot therefore release to open the chain starting circuit the second call is not therefore mutilated.

Setting code register for first ofiice code letter As soon as the position finders of Fig. 3 have associated an idle sender with the operators position equipment, circuits are effective forsetting the relays 803, 804, 807 and 808 of the oflice code register of the sender.

At the operators position equipment upon the operation of the unitscode register relay 201 a circuit was established for operating the transfer relay 400 extending from ground at the outer left front contact of relay 201,

over the inner rightback contact ofrelease relay 205, conductor 411, the right back con? tact of counting relay 406, the left back contact of counting relay 401, thence to battery through the winding of relay 400. It will first be assumed that both a first and second select-or such as shown in Figs. 9 and 10 are to be operated to select a trunk to the desired dial switching miles in response to the office code letters C, A, the letter C corresponding to the digit 2. For this purpose the armature contacts of. the tens ofiice code register relay 202 of Fig. 2, which was operated in response to the depression of the'oflice key 200,are cross-connected in such a manner as to operate the code register relay 804 ofthe.

sender over a circuit extendin from batter through the winding of relay 804, conductor 2 819, the intermediate right back contact of relay'504, conductor 506, the inner left contact of relay 341, brush: 327, conductor 231, the inner lower front contact of transfer relay 400, conductor 402,-to ground at the inner left contact of register relay 202. V

In order to register digits corresponding to all of the code letters used in office codes,

four register relays 803, 804, 807 and 808 are employed in the sender which may be operated individually and in combination over circuits extending in the manner previously traced for relay 804 to grounded armature contacts of the code register relays of Fig. 2. To enable a better understanding of the manner in which the code digits may be registered in the sender the following chart has been prepared.

The vertical column'of figures at the left of the chart indicates the digits corresponding to ofiice' code letters that may be registered by the oflice code relays. The numbers in the sub-divisions of the chart opposite this vertical column indicate the relays of the sender register which are operated for the corresponding digits to be registered and the numbers above each vertical column of the chart indicate the conductors of Fig. 2 which maybe variously grounded by the register relays of Fig. 2 to operate the register relays offthe sender. Thus, for example, if the digit 8 is to be registered, by reading horizontally across the chart it will be apparent that register relays 803, 804 and 807 must be operated in combination and that to operate these relays a tens code relay of Fig. 2 must be operated which will ground conductors 405, 402 and 403 or a units code relay which will ground conductors 410, 408 and 407.

Operation of first selector in accordance with first code letter With the register relay 804 operated a pulsing circuit extending from the first selector of Fig. 9 may be traced from battery through the winding of relay 904, back contact of rotary-magnet 905, back contact of vertical magnet 903, inner right back contact of relay 906, intermediate right back contact of relay 907, conductor 908,.outer right back contact of relay 809, back contact of the counting relay 810, conductor 811, back contact of relay 601, winding of relay 602, inner left back contact of relay 600, left back contact of relay 603, conductor 812, left contact of relay 804, conductor 604, normal terminal of brush 514 of steering switch 550, conductor 515 to ground at the inner right contact of relay 600. Relays 602 and 904 energize in this circuit,relay 602 upon energizing closing a circuit from ground at its front contact, over the outer left back contact of relay 605, conduct-or 606, brush 516 and normal terminal of switch 550, conductor 517, right front contact of register relay 804, right back through the winding of relay 814, over the front contact of relay 832 to ground'on conductor 806, but relay814 does not energize until relay 602 deenergizes and removes the shunting ground from its winding.

At the selector of Fig. 9 upon the energization of relay 904 a circuit is closed for the vertical magnet 903, from battery, through the winding of magnet 903, the outer right front contact of relay 900 to ground at the inner left front contact of relay 904. Relay 904 also closes an obvious circuit for relay 909 which disconnects thetip and ring brushes of the selector during its vertical selection movement- Magnet 903 energizes and at its contact opens the previously traced pulsing circuit through the winding of relay 904 and the winding of relay 602. The selector switch is thus stepped vertically one step, opening at the off-normal contacts 901 the initial enercircuit of relay 900. Upon the open ing of the pulsing circuit and the deenergization of pulsing relay 602 the shunt around the counting relay 814 is opened and such relay energizes in the locking circuit of relay 832, extending the counting relay lead 813 over its front contact, the back contact of counting relay 816, conductor 817, brush 518 and normal terminal of steering switch 550, conductor 519, the right back contact of register relay 807, to battery, through the winding of counting relay 818. Relay 818 energizes upon the next closureof the pulsing circuit and the consequent"energization of relay 602, and looks through the windings of relays 802 and 810 in parallel, over the front contact,

810 opening the pulsing circuit, extending as previously traced to the first selector and relVhen the puls ing circuit is again opened and relay 602 deenergizes, relays 802 and 81-0 energize, relay lay 802 opening the previously traced circuit extending through the winding of magnet 512. Magnet512 now deenergizes advancing the steeringswitch 550 into its second position. u

l/Vhen the steering switch leaves position 1 the circuit of relay 805 is opened and such relay releases, removing ground from conductor 806, thereby releasing the operated counting relays. A circuit is now established for relay 603,v extending fromv battery, through the winding of said relay, conductor 608, the second position terminal and brush 503 of steering switch 550, conductor 502 to ground at the outer intermediate contact relay 621; A circuit is also established for relay 640, through the second position terminal and brush 520 of steering switch 550,conductor 521 to ground at the left back contact of relay 617. Relay 640 looks over its right contact to ground at the back contact of relay 505 and closes a circuit for relay 4-01 of the operators position circuit extending from 7 battery, through the winding of relay 401, the

left back contact of relay 406, conductor 418,

brush 329, the next to outer left contact of lay 341, conductor 346, to ground at the left contact of relay 640. Belay 401 operates in this circuit locking through the winding of relay 406, and the right front contact of relay 401 to ground on conductor 411, but relay 406 being shunted by ground on conductor 418 does not operate at this time. 7 At its left back contact relay 401 now opens the circuit of transfer relay 400 and closes a circuit for contacts of the tens code register re transfer relay 419, extending from battery, through the'winding of relay 419, the left front contact of relay'401, the right back contact of relay 406 to ground on conouctor 411. Relay 400 upon deenergizaing discon s the conductors 402 to 405 inclusive exte i relay 419 connects the conductors 40' to 410 inclusive extending to the contacts of the code register relays preparatory to the tran ring of the units code letter to the sender. When relay 400 disconnects the conductor 402 the code register relay 804' of the sender releases.

First selector hunts for idle second selector relay 907, the outerright back contact of re lay 906, the inner right frontcontact and right winding of relay 900, which is wound differentially to the left winding thereof,

commutator brush 911 to ground on terminal 912 of the commutator corresponding tothe second vertical level of the banks of the first selector which level of terminals has been assumed to be connected to terminals of trunks extending to second selectors such as the one shown in Fig; 10. Relay 609 operates in this circuit and closes a circuit for relay 614 extending from battery, winding of relay 614, front contact of relay 609 to ground on conductor 509. Relay 614 upon operating shunts at its left front contact the left winding of relay 609, thereby increasing the current flowing through the right winding ofrelay 900, whereupon relay 900 differentially releases, removing the vertical magnet 908 from the control of stepping relay 904, Relay 900 also connects the right wind- 7 ing of relay 609, over the circuit previously traced to the inner right back contact of relay 900, thence to battery, through resistance 913, overthe back contact of rotary magnet 905. Relay 609 thereupon releases and at its front contact opens the previously'traced circuit of relay 614; Since relay 614 is slow to release a circuit is momentarily closed upon the release of relay 609 from ground on con-' ductor 509, over the back contactvjof relay 609, the right front contact of relay 614, to

battery, through the winding of rela 610 VW'll'lCll thereupon energizes and 100 s to contact and at its outer right front contact close a circuit for relay 615, extendingfrom 'rcund therethrough, over the outer'right. rront contact of relay 610, conductor 611,,

the outer back contact of relay 805, conductor 612, thence as traced to battery, through resistance 918 at the firstselector. Relay 615' operates n turn operating relay 616, overa circuit extending from battery, through the winding of relay 616, the inner left back con tact of relay 605, to ground at the contact of relay 615. Relay 616 upon operating locks over its left contact to ground at the back contact of pulsing relay 602 and at its right contact establishes an obvious circuit for re lay 617, which relay in turn establishes a circuit for magnet 512 of the steering switch 550, extending from battery, through the magnet 512, over conductor 513, the inner right back contact of relay 504 to. ground at the 1 ft front contact/of relay 617. Belay 617 also its front contact closes a circuit for relay 605, extending from battery, through the winding of relay 605, the right front contact of relay 617,,to ground at the right back contact of relay 622.

A circuit is now established for the stepping relay 904 of the first selector, extending from battery, through the winding of relay 904, back contacts of rotary magnet 905 and 'vertical magnet 90?), back contacts of relays 906 and 90?, conductor 908, outer right back. Contact of relay 809, back contact of count lng relay 810, conductor 811, back contact of relay 601, winding of sender pulsing relay 602, inner left contact of relay 600, left front contact of relay 603, the left front contact of relay 610, the right front contact of relay 605, conductor 632, the second position terminal and brush 514 of steeringswitch 50, con

ion

ductor 515 to ground at the inner right contact of relay 600. Relays 904 and 602 operate in this circuit. Relay 904 upon energizing closes the circuit of relay 909 to disconnect the tip and ring brushesof the selector during its rotary hunting movement and closes the circuit of rotary magnet 905 which may be traced from battery, through the winding of magnet 905, the outer right back contact of relay 900 to ground at the inner left contact of relay 904. Magnet 905 upon energizing in turn opens the previously traced circuit for relays 904 and 602, relay 904 in turn opening the circuit of magnet 905. Thus relay 904 and magnet 905 cooperate with each otherto cause the step-bystep rotation of the first selector brushes over the selected second level in search of an idle second selector.

At the sender upon the energization of pulsing relay 602 the holding circuit of re lay 616 is opened at the'back contact of relay 602 and relay 616 deenergizes in turn opening the initial energizing circuit of relay 617. Relay 617 being slow to release, however, does not release before a holding circuit is established therefor from battery, through its winding, the outer left front contact of relay 605, to ground at the front contact of relay 602. Therefore as long as relay 602 continues to receive impulses of current due to the hunting movement of the first selector relay 617 is held energized and in turn maintains relay 605 operated. Relay 615 is at this time deenergized since its operating circuit was opened at the back contact of rotary magnet 905 upon the first energization of magnet 905 and the initial operating circuit of relay 616 is therefore opened at the contact of relay 615.

When an idle second selector is found a circuit is established for relay 1015 extending from battery, winding of relay 1015, conductor 918, terminal 919, brush 920, next to inner back contact of relay 909, conductor 921,

back contact of relay 820 to ground on conductor 721. Relay 1015 energizes connecting locking ground for the relays of the second selector and opening at one pointthe circuit of the release magnet 1017. Another circuit is also established from battery, through the left winding of relay 1000, off-normal contacts 1001, conductor 1002, terminal 922, brush 914, the outer left back contact of relay 906, the back contact of release magnet 917, inner right back contact and right winding of relay 907, conductor 902, winding of relay 800, conductor 801 to ground at the inner left contact of relay 621. Relays 1000 and 907 operate in this circuit but due to its small number of turns relay 800 does not operate. Relay 1000 upon operating locks over its left contact to ground at the front contact of relay 1015 and at its outer right front contact prepares the operating circuit of the vertical magnet 1003. Relay 907 upon operating at the front contact of relay 915, at its left back contact opens the energizing circuit for relay 906 and at its inner right back contact opens its own initial energizing circuit, and connects the trunk conductors 908 and 910 over its outer and intermediate right front contacts, right back contacts of relay 909, ring and tip brushes 923 and 924 to the selected trunk conductors 1008 and 1010. At its inner right front contact relay 907 connects ground on conductor 902, over the back contact of release ma gnet-917 the outer left back contact of relay 906, brush 914, terminal 922, to conductor 1002. At its intermediate right back contact relay 907 also opens the circuit previously traced through the windings of relays 904 and 602 whereupon these relays are released. Pulsing relay 602 upon releasing opens the holding circuit of slow to release relay 617 which in turn releases relay 605. Relay 617 upon releasing also opens the circuit of magnet 512 which advances the brushes of steering switch 550 into contact with the third position terminals of their associated arcs. As soon as the steering switch leaves position 2 the circuit of relay 603 is opened and that relay releases, opening the holding circuit of relay 610 which also releases. With the steering switch in position 3 the previously traced circuits-for relay 805 and stepping magnet 512 are again established and magnet 512 energizes preparatory to advancing the steering switch another step. 1

Sette /cg the second selector in accordance wzth second 077206 code letter registered in sender It has been assumed that the second code letter registered on the code register relays of the operators position was A, having a numerical equivalent of 2, and that the units register relay 201 was energized by the depression of key 200. The armature contacts of relay 201 are cross-connected to conductors 407 to 410 inclusive in such a manner that conductor 408 is grounded to operate that the sender code register relays 803, 804,

807 and 808 are operated singlyand in combination in accordance with the foregoing table, over conductors 407 to 410 inclusive to register the units code digit in the same manner as previously described in connection 

